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Current Transformers 2015 Current Transformers A current transformer is an instrument that transforms one current value to another current value (e.g. 100A to 5A.) The advantage of using a current transformer in an industrial context is that it provides galvanic isolation from the voltage on the primary winding while simultaneously furnishing a power signal that has been converted to a standard level (1A or 5A), which in turn permits the use of standard measurement instruments and relays. Standardmodels Noratel offers a comprehensive range of current transformers which were previously marketed under the name “Garre”. Standard models are available as encapsulated versions (UL 94-V0) in a myriad of different flavors all manufactured and tested according. IEN60044-1 (VDE 0414/1). A complete list of Noratels standard range of power supplies are available in a separate electronic catalog (pdf) and at the www.noratel.com When current transformers are being ordered, the supplier needs to know: ■ ■ ■ Custom designed current transformers In addition to our comprehensive standard product line of current transformers, customised designs and solutions are available to customer specifications and designed and manufactured in accordance with specified standards (IEC, ANSI, BS). Current transformers can be supplied for primary currents of from 10 Amps to 10000 Amps and in accuracy classes from 0.1% and higher for specified burdens and overcurrent values. Micafil bushings with paper insulated ushing current transformers mounted in aluminium housings ■ ■ ■ ■ Desired ratio - primary current and secondary current (For example 500A/5A) Centre hole in the transformer/Dimension of the primary conductor - will a rail or cable be used? (Example: Rail 10x50mm or ID>50mm) Desired burden (power) (VA) and accuracy class (Example: 20 VA cl. 0.5 (see IEC 60044-1)) Overcurrent factor must be specified for relay transformers and may be specified for instrument transformers Distance between primary conductors in 3-phase system If special fastening arrangements are desired (Fastening holes for screws, DIN rail fasteners, etc.) Specify whether it is an instrument or relay transformer (this is often evident from the given class specification) A minimum specification for a relay transformer with a ratio of 1000A to 5A, burden 30VA, accuracy class 5%, overcurrent factor 20 (20 times the rated current) and central hole of min. 50mm would look like the following: 1000/5A 30VA kl.5 P20 ID>50mm A corresponding specification for an instrument transformer in a Window type transformer application, with a ratio of 400A to 5A, burden 10VA, accuracy class 0.5%, overcurrent factor 5 (5 times the rated current) and centre hole with min. dia. 30mm, would look like the following: 400/5A 10VA kl.0,5 Fs5 ID>30mm Epoxy moulded transformers with connection points and alternative means of fixing and fastening 54 www.noratel.com 2015 Current Transformers Current transformers General specifications Noratel current transformers Current transformers can be delivered with fastening brackets and sealable secondary housings. Moulded and encapsulated styles, manufactured and tested in accordance with IEC 60044-1, which also encompasses the VDE 0414 norm. Alternatively in accordance with IEEE Std C57.13-1993 (ANSI) ■ ■ ■ ■ ■ ■ ■ Standardmodels Hole Max. operating voltage: Test voltage (1 min): Frequency: Continuous overcurrent: Thermal overcurrent (1 sec): Dynamic overcurrent: Insulation class (ta): Dim. (BxDxH) 720 V 3 kV 50/60 Hz 1,2 x IN Ith = 60 x IN Idyn = 2,5 x Ith E (120°C) Type Ratio Burden GK 250/5 A 0,1 - 2 VA 74x52x81 mm 4-083-000372 GK 300/5 A 0,1 - 2 VA 74x52x81 mm 4-083-000172 GK 400/5 A 0,1 - 3 VA 74x52x81 mm 4-083-000173 GK 500/5 A 0,1 - 5 VA 74x52x81 mm 4-083-000375 GK 600/5 A 0,1 - 5 VA 74x52x81 mm 4-083-000167 40x10 mm 30x15 mm Ø 29 mm. L60X 500/5 A 0,1 - 3 VA L60X 1000/5A 0,1 - 7,5 VA L60X 1500/5 A 0,1 - 10 VA K100K 1000/5 A 0,1 - 5 VA K100K 1500/5 A 0,1 - 5 VA K100K 2000/5 A 0,1 - 5 VA K100K 2500/5 A 0,1 - 5 VA K100K 3000/5 A 0,1 - 5 VA LGK 3000/5 A 0,1 - 5 VA LGK 4000/5 A 0,1 - 5 VA 60x10 mm 50x20 mm 40x30 mm Art. no. 89x50x108 mm 4-083-000204 89x50x108 mm 4-083-000206 89x50x108 mm 4-083-001098 139x54x150 mm 4-083-000582 139x54x150 mm 3-083-000755 139x54x150 mm 3-083-000756 139x54x150 mm 3-083-000757 139x54x150 mm 3-083-000758 120x35 mm 170x54x140 mm 3-083-000737 120x35 mm 170x54x140 mm 3-083-000738 100x10 mm 80x60 mm Meter switcher - IP00 Type N-MOK In systems incorporating current transformers, it is necessary for the secondary side to be easily short-circuited when the meter is taken down for auditing or replacement. Meter switchers allow the technician to perform the requisite measurements in a fast, simple and safe manner without disturbing the rest of the circuitry. Standardmodels Type Description Art. no. N-MOK230 230 Volt, 3-phase meter switcher with 2 current systems 3-083-000238 N-MOK400 400 Volt 3-phase meter switcher with 3 current systems 3-083-000237 www.noratel.com 55